Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface; and,

FIG. 2 is a front view of another embodiment of a display screen or portion thereof with a graphical user interface.

The broken lines illustrate portions of the article and portions of the graphical user interface. None of the broken lines form part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 